A phytochemical investigation on the aerial parts of <i>Euphorbia helioscopia</i> resulted in the isolation of 27 macrocyclic diterpenoids, including three previously unreported lathyrane derivatives, euphohelioscopoids A-C (<b>1</b>-<b>3</b>). Their structures were elucidated by spectroscopic data interpretation. Three jatrophanes, euphoscopin C (<b>4</b>), euphorbiapene D (<b>6</b>), and euphoheliosnoid A (<b>5</b>), showed cytotoxicity against a paclitaxel-resistant A549 human lung cancer cell line with IC<sub>50</sub> values of 6.9, 7.2, and 9.5 μM, respectively, but were inactive against the parent A549 human lung cancer cell line (IC<sub>50</sub> > 10 μM). It was found that jatrophanes with a benzoyloxy or a nicotinoyloxy substituent at C-7 showed more potent cytotoxic activity than their analogues containing acetyloxy and hydroxy groups at this position.